Related: There's [a proposal][1] for `Reflect.isConstructor` (and `Reflect.isCallable`) which addresses this very gap. There seem to be some questions around `Reflect.isCallable` (whether it should be true or false for class constructors, since you can't [[Call]] them), but I didn't see issues raised around `Reflect.isConstructor`. Seems a bit stalled, though.
[1] https://github.com/caitp/TC39-Proposals/blob/master/tc39-reflect-isconstructor-iscallable.md -- T.J. On Mon, Jan 16, 2017 at 5:00 PM, Michael Haufe <[email protected]> wrote: > The question came up recently on CLJS [1] on how to determine if an object > is safe to call as a Constructor. > > Traditionally one uses try {... x = new foo() ... } catch(e) { ... x = > foo() } > > > In the list of well-known symbols [2] there doesn't seem to be a way to > reference [[Construct]] to perform a test to avoid the try/catch. In the > following[3] though there is reference to Symbol.create which doesn't seem > to be in the spec but seems to be the one to look for. Can we get > clarification on if it is possible to determine if an object can be > constructed before attempting it? > > [1] <https://groups.google.com/forum/#!msg/comp.lang. > javascript/nSesJfznwjg/rKiQOzkYEwAJ> > [2] <http://www.ecma-international.org/ecma-262/7. > 0/#sec-well-known-symbols> > [3] <https://github.com/lukehoban/es6features/blob/master/ > README.md#subclassable-built-ins> > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > >
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